This invention relates in general to inflatable cushions, and more particularly to inflatable cushion having normally isolated zones and a valve for placing its normally isolated zones in communication.
Those individuals who are confined to wheelchairs run the risk of tissue breakdown and the development of pressure sores, which are extremely dangerous and difficult to cure. Typically much of the individual's weight concentrates in the regions of the ischia, that is at the bony prominences of the buttocks, and unless frequent movement occurs, the flow of blood to the skin tissue in these regions decreases to the point that the tissue breaks down. Cushions which are especially designed for wheelchairs exist for reducing the concentration of weight in the region of the ischia, and these cushions generally seek to distribute the user's weight more uniformly over a larger area of the buttocks.
Perhaps cellular cushions provide the most uniform distribution of weight and thus provide the greatest protection from the occurrence of pressure sores. These cushions have an array of closely spaced air cells which project upwardly from a common base. Within the base the air cells communicate with each other, and thus all exist at the same internal pressure. Hence, each air cell exerts essentially the same restoring force against the buttocks, irrespective of the extent to which it is deflected. U.S. Pat. No. 4,541,136 shows a cellular cushion currently manufactured and sold by ROHO, Inc., of Belleville, Ill., for use on wheelchairs.
In a sense the typical cellular cushion provides a highly displaceable surface which tends to float the user. While this reduces the incidence of pressure sores, it detracts from the stability one usually associates with a seating surface. Most of those confined to wheelchairs have little trouble adjusting to the decrease in stability, but for those who have skeletal deformities, particularly in the region of the pelvis and thighs, and for those who lack adequate strength in their muscles, lesser stability can be a source of anxiety. A variation of the ROHO cellular cushion addresses this problem with totally isolated zones and also cells of varying height. By varying the pressure between zones, one can accommodate for skeletal deformities while still maintaining satisfactory protection against pressure sores. U.S. Pat. No. 4,698,864 shows a zoned cellular cushion with cells of varying height.
Typically, a zoned cellular cushion has a separate filling stem and valve for each of its zones. The user simply opens the valve of each stem and introduces air into the zone for that stem, usually with a hand pump, and then releases the air from the zones until the desired posture is achieved. In a more sophisticated arrangement, a hose kit connects a single pump to a manifold which in turn is connected to the several valves through separate hoses. These hoses are fitted with separate hose clamps so that the air from the pump may be directed to the cells of the individual zones independently, and likewise the air can be released from them independently, all by manipulating the clamps. The hoses of the hose kit lie externally of the cushion and may become entangled in components of a wheelchair. Furthermore, by reason of their remote location, the hose clamps are difficult to manipulate.
Even more traditional inflatable cushions derive advantages from zoning, that is from being divided into zones or compartments which can be isolated from each other to accommodate skeletal deformities.
The present invention resides in a zoned inflatable cushion and in a valve that forms part of the cushion and facilitates the distribution of air within the cushion, particularly between the zones of the cushion.